Vibrational effects on the electron momentum distributions of valence orbitals of formamide

Abstract

The ionization energy spectra and electron momentum distributions of formamide were investigated using the high-resolution electron momentum spectrometer in combination with high level calculations. The observed ionization energy spectra and electron momentum distributions were interpreted using symmetry adapted cluster-configuration interaction theory, outer valence Green function, and DFT-B3LYP methods. The ordering of 10a(') and 2a(") orbitals of formamide was assigned unambiguously by comparing the experimental electron momentum distributions with the corresponding theoretical results, i.e., 10a(') has a lower binding energy. In addition, it was found that the low-frequency wagging vibration of the amino group at room temperature has noticeable effects on the electron momentum distributions. The equilibrium-nuclear-positions-approximation, which was widely used in electron momentum spectroscopy, is not accurate for formamide molecule. The calculations based on the thermal average can evidently improve the agreement with the experimental momentum distributions.

Vibrational effects on valence electron momentum distributions of CH2F2

“…Thus, the vibrational effects observed at p ∼ 0 may be attributed mainly to the zero point vibrations of the ν 6 and ν 7 modes. Although vibrational effects have generally been considered to be due to thermally induced nuclear motions, 31,33,[35][36][37] it can be deduced from the above discussion that this is not the case for the 2b 1 ionization process; molecular vibration plays a crucial role in the ionization process even at T = 0 K. Indeed, an additional calculation at T = 0 K has shown that difference between the 2b 1 momentum profiles for T = 0 and 298 K is negligibly small.…”

“…20,23,26,[31][32][33] Besides most of the investigations reported so far have examined only a few of vibrational modes. Under these circumstances, we have recently developed a method to calculate electron momentum profiles with contributions from all the vibrational modes being involved and applied it to ethylene.…”

Theoretical study of molecular vibrations in electron momentum spectroscopy experiments on furan: An analytical versus a molecular dynamical approach

“…These motions may indeed explain numerous discrepancies between theory and experiment, precisely in cases where the PWIA was assumed to break down. For instance, two recent and pioneering studies on formamide and ethylene, by Miao et al 72 and by Watanabe et al, 73 respectively, have shown that specific vibrational motions can noticeably affect valence orbital momentum distributions, in the form of significant turn-ups of (e,2e) ionization intensities at low electron momenta. The latter study was based on a decomposition of contributions arising from each quantized vibrational eigenstates to the momentum distributions of interest within the frame of the (rigid-rotor-) harmonic oscillator approximation.…”

Temperature-Dependent Electron Momentum Spectroscopy on the Molecular Orbitals of Dimethyl Ether

“…Although the equilibrium geometry approximation by eq has been widely used to analyze the experimental data, recent EMS studies have shown that molecular vibration may appreciably affect the momentum profiles of polyatomic molecules. − In order to take the vibrational effects into account, we have developed a theoretical method, which is referred to as the harmonic analytical quantum mechanical (HAQM) approach . Details of the approach are given elsewhere − and not repeated here.…”